The knowledge of our human origins has taken a huge leap forward after anthropologists decoded the DNA of a bone as old as 400,000 years old, revealing that our ancestors may have had sex with more species of early humans than previously thought.

A bone was dug up at what appears to be an ancient burial site in
Sima de los Huesos, in Spain. Its genome indicates that the early
European was more closely related to a much earlier species of
human dating as far back as 700,000 years ago than to our
immediate ancestors, the Neanderthals. Neanderthals lived as
recently as 30,000 years ago, before humankind’s modern
incarnation, Homo sapiens, appeared on the scene. Homo sapiens
were previously thought by scientists to have interbred with
Neanderthals, but not with other hominid species.

The bone owes its good condition to the subterranean climate in
the northern highland area of Sierra de Atapuerca. The find was
at a depth of about 30 meters, where the temperature is a little
more than 10 degrees Celsius.

Svante Paabo, director of the Max Planck Institute for
Evolutionary Anthropology in Leipzig, Germany, was one of the key
participants in the research, which was published in the journal
Nature. He points out that the results extracted from the study
of the bone “show that we can now study DNA from human
ancestors that are hundreds of thousands of years old.”

That is a substantial achievement in itself, as such old DNA had
until now only been studied when found in permafrost – mountain
soil that is frozen over and allowing for preservation of bones
and flesh, like the ones we often find when conducting animal
studies.

But the technique does little to reduce the mystery the
anthropologists are faced with now.

Sima de los Huesos – in English it can be translated as ‘Pit of
Bones’ – is famous for harboring the largest collection of
hominid fossils dating back anywhere from 100,000 to 700,000
years ago, to the Pleistocene period. Scientists have so far
discovered 28 skeletons.

The individuals found there were previously thought to be
ancestors to Homo heidelbergensis, which itself is thought to be
a common ancestor to us – Homo sapiens – and our immediate
cousins, the Homo neanderthalensis (Neanderthals).

According to later studies, Paabo and team assumed that this bone
would share an ancestor with the Neanderthals.

But what the bone’s mitochondrial DNA (mtDNA) revealed after a
couple of grams of bone powder were studied were more questions
than answers.

They went about sequencing the genome from the mtDNA, which is
passed down through the maternal line, and found a mysterious
relation, after comparing their results with the modern human
one, then that of an ape, a Neanderthal and a Denisovan.

The last on that list is a mysterious, recently discovered branch
of Asian hominids considered to be a sister group to the
Neantherthals. Therein lay the surprise: the studied sample was
found to have a stronger relationship to the far-more distant
Denisovans than to the Neanderthals, which still roamed the Earth
some 30,000 years ago.

To put this into perspective, the previous oldest bone we have
studied belongs to a Denisovan that dates back to 80,000 years
ago – and is also the oldest DNA we had studied until now.

Furthermore, this comes on the heels of another recent and no
less staggering
revelation.

"The fact that the mtDNA of the Sima de los Huesos hominin
shares a common ancestor with Denisovan rather than Neanderthal
mtDNA is unexpected since its skeletal remains carry
Neanderthal-derived features," said Matthias Meyer, a
co-author of the study.

This could mean one of several things: that the newly discovered
Spanish bone could belong to an ancestor of both the Neanderthals
and the Denisovans; another is that an entirely new branch of
hominids is in question – one related to the Denisovans.

Director at the Center for Research on Human Evolution and
Behaviour in Madrid, Juan-Luis Arsuuga explained the result as
pointing to a “complex pattern of evolution in the origin of
Neanderthals and modern humans.”

This is just the latest in a series of startling recent
discoveries that put into question our origins, pattern of
movement, as well as inter-breeding.